U.S.Secretary of State John Kerry met with the foreign ministers of France, Britain, Italy, and Germany – along with EU foreign policy chief Federica Mogherini -- in Paris on March 13.

A top item on the agenda was the UN-sponsored indirect peace talks due to begin in Geneva on March 14 between Syrian President Bashar al-Assad’s regime and representatives of Syrian opposition factions.

Those talks are aimed at capitalizing on a shaky truce between Syrian government forces and opposition fighters.

Kerry, speaking in Paris, warned the Assad regime and allies against exploiting the truce.

"If the regime and its backers think they can test boundaries, diminish their compliance in certain areas, or act in ways that call into question their commitment to the cessation -- without serious consequences for the progress we have made -- they are mistaken," Kerry said.

Kerry also said IS militants in Syria were being weakened.

"In Syria, over the last three weeks alone, [the IS] has lost 3,000 square kilometers and 600 fighters," he said.

Al-Qaeda militants and IS fighters are not included in the truce deal and will not be represented at the Geneva talks.

UN peace envoy Staffan de Mistura has said the Geneva meetings would not last more than 10 days.

Russia had called on de Mistura to include Syrian Kurds in the Geneva peace talks.

De Mistura told the Swiss newspaper Le Temps that while Syrian Kurds would not take part, they should be given a chance to express their views.

The negotiations are set to cover the formation of a new Syrian government, a fresh constitution, and the organization of UN-monitored presidential and parliamentary elections within 18 months.

The High Negotiations Committee, a Saudi-backed umbrella opposition group, said it will attend the Geneva talks and press for a transitional government with full executive powers that does not include Assad or any of his close associates.

Chief opposition negotiator Muhammad Allush said in Geneva on March 12 that "the transitional period should start with the fall, or death, of Bashar al-Assad."

Allush said a transitional government "cannot start with the presence of the regime, or the head of this regime still in power."

Syrian Foreign Minister Walid al-Muallam said Assad's delegates would head to Geneva on March 13.

But Muallam said on March 12 that the oppoition's calls for Assad's ouster would be a "red line" and suggested that it would lead to the end of the indirect negotiations in Geneva.

Muallam said: "We will not talk with anyone who wants to discuss the presidency.... Bashar al-Assad is a red line. If they continue with this approach, there's no reason for them to come to Geneva."